How long does it take for a Vessel to reaquire aggro from tentacles? (Illaoi)

I am trying to learn every aspect of playing and countering Illaoi, but I still can't figure out one thing: When a target becomes a vessel (by killing their spirit or if they run away from their spirit), they attract the aggro of all the nearby tentacles. But once the tentacle hit them once, they stop hitting them for a while. Has anyone figured out how long? :)

Cheers.